Field of the Invention
The present invention relates generally to the field of fiber optics, and in particular to an improved grating-based fiber optic sensor.
Background Art
Grating-based fiber optic sensors are used in a number of different applications to measure temperature, strain, pressure, vibration, fluid level, and the like. Fiber-based sensing technology has a number of advantages over electric sensors, including, for example: small size, high sensitivity, and remote operation. In addition, fiber optic sensors do not send electrical power to the sensor location and do not conduct electricity; they are thus immune to electromagnetic interference. In grating-based fiber optic sensors, the sensing function is provided by fiber Bragg gratings (FBGs), which have a wavelength response that is sensitive to a number of parameters applied to the sensor, including temperature and strain.
Typically, in an environment that is rich in certain gases, such as hydrogen or deuterium, the diffusion of these gases through a fiber optic sensor not only causes the fiber components to experience insertion losses, but also changes the fiber properties, such as the effective refractive index. These unwanted insertion losses and index changes typically lead to measurement accuracy problems, respectively, for intensity-based and wavelength-based fiber optic sensors.
To combat this gas diffusion problem, a number of possible solutions have been explored, including: designing fibers to be less susceptible to particular gases; designing sensor packages to block the gases from entering the sensor body; and providing an additional sensor for gas monitoring. However, these technologies typically have only been able to either improve the sensor performance by a relatively small amount or have thus far not been cost-effective.